1. Field of the Invention
The present invention relates to a glossiness processing apparatus, and more particularly, to a glossiness processing apparatus that performs glossiness processing for forming an image of high glossiness on a sheet.
2. Description of the Related Art
In recent years, color images have been formed for increasingly diverse purposes, and hence, image forming apparatuses such as a color printer, a color copying machine, a facsimile, and a compound machine using a digital electrophotographic printing method are spreading widely. Further, recently, the quality of the color image has been enhanced, so the image forming apparatuses is widely used more often for outputting an image of a digital still camera whose recent spread on the market is prominent.
Under such circumstances, as image forming apparatuses such as a printer and a copying machine using the electrophotographic printing method or the like, there is a demand for those capable of outputting an image of high-glossiness quality comparable to that of a silver halide photography, as well as outputting an image of ordinary quality.
As an example of an image forming method of obtaining a color image of high glossiness, for example, there is a method as described in Japanese Patent Application Laid-open No. H05-216322. According to this method, a sheet serving as a transfer material travels below a member containing a heat source by a belt-shaped conveying member, whereby color toner adhering to a transparent resin layer made of a thermoplastic resin on a sheet surface is heated to melt the color toner in the transparent resin layer. Next, the color toner is cooled to be fixed on the sheet, whereby an image is formed. After the color image is thus formed, the sheet is separated from the belt-shaped conveying member.
In the high-gloss image forming method, as described in Japanese Patent Application Laid-open No. 2002-99168, the belt-shaped conveying member bringing a sheet into contact therewith is positioned below the sheet while the sheet is brought into contact with the belt-shaped conveying member. It has also been proposed that the belt-shaped conveying member be positioned above the sheet.
Further, as a configuration of an image forming apparatus capable of obtaining a color image of high glossiness adopting such a method, there is a configuration in which in addition to a fixing portion (hereinafter, referred to as a first heating portion) for performing ordinary fixing processing, a second heating portion having a belt-shaped conveying member are provided. The second heating portion heats again a sheet fixed by the first heating portion, whereby an image of high glossiness is obtained.
In this case, for example, as described in Japanese Patent Application Laid-open No. 2004-151201 and Japanese Patent Application Laid-open No. 2003-005545, an external processing apparatus provided with a second heating portion serving as a re-heating processing system is connected to the image forming apparatus. Further, a small fixing portion having a belt-shaped conveying member of a photographic size may be provided in a space of a sheet discharging portion (so-called in-body sheet discharging portion) between an image forming portion and an image reading portion of the image forming apparatus.
In this case, the external processing apparatus having the second heating portion passes through an ordinary image forming process, and receives a sheet discharged after being fixed by the first heating portion of the image forming apparatus. In a case where an image of high glossiness is selected, the external processing apparatus performs re-heating processing. When such an external processing apparatus receives a sheet, the external processing apparatus conveys the sheet to the second heating portion having a belt-shaped conveying member through a branch path provided inside, in the case where an image of high glossiness is selected.
Then, the external processing apparatus heats and presses the sheet conveyed to the second heating portion with heating means and pressing means under the condition that a high-glossiness formation surface is in contact with a belt surface of the belt-shaped conveying member, thereby discharging the sheet with an image of high glossiness formed thereon. In the case where an image of high glossiness is not selected, the external processing apparatus switches the branch path to a discharging tray side, thereby discharging the sheet without performing any other process.
In a conventional image forming apparatus with such the second heating portion, for example, in a case where the second heating portion is mounted to an in-body sheet discharging portion, a system configuration can be realized in which an image of high quality made of a high-gloss image is obtained without enlarging the mounting area of the image forming apparatus. However, in the case where the second heating portion is set in the in-body sheet discharging portion, the second heating portion needs to be downsized, and in this case, the size of a sheet that can be fixed is limited, which makes it difficult to receive sheets of various sizes.
On the other hand, in a case where a separate external processing apparatus is attached to an image forming apparatus, a second heating portion having a belt-shaped conveying member can be enlarged. Therefore, glossy images of various sizes can be obtained. However, in this external processing apparatus, a conveying path is placed horizontally, so there is a problem that the width in a sheet conveying direction of the fixing apparatus becomes large to enlarge the apparatus and widen the setting area. In particular, as the belt-shaped conveying member is made longer so as to enlarge the second heating portion, the apparatus is more enlarged.